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Set default temperature to None instead of 0.0#1989

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fix-default-temperature-to-none
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Set default temperature to None instead of 0.0#1989
neubig wants to merge 22 commits intomainfrom
fix-default-temperature-to-none

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@neubig neubig commented Feb 10, 2026

Summary

Change get_default_temperature to return None by default instead of 0.0. This allows models to use their provider's default temperature setting rather than forcing temperature=0.0 for all models.

Motivation

As discussed in #1913, always setting temperature=0.0 causes issues with some models (like claude-4.6) that don't accept this value. By returning None, we let the provider use their own default temperature, which:

  1. Avoids errors from providers that don't accept certain temperature values
  2. Ensures new models work out of the box without needing explicit configuration
  3. Simplifies the codebase by removing unnecessary default values

Changes

  • get_default_temperature() now returns float | None instead of float
  • Default return value changed from 0.0 to None
  • Models with specific temperature requirements (kimi-k2-thinking, kimi-k2.5) still explicitly return 1.0
  • Updated field description in LLM class to reflect the new behavior
  • Updated tests to expect None instead of 0.0

Testing

All 583 LLM tests pass. Pre-commit hooks pass on all modified files.

Fixes #1913

@neubig can click here to continue refining the PR


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Change get_default_temperature to return None by default instead of 0.0.
This allows models to use their provider's default temperature setting
rather than forcing temperature=0.0 for all models.

Models with specific temperature requirements (kimi-k2-thinking, kimi-k2.5)
still explicitly return 1.0.

Fixes #1913

Co-authored-by: openhands <openhands@all-hands.dev>
@neubig
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neubig commented Feb 11, 2026

@OpenHands check the failing CI, merge main, reproduce locally, and fix any issues.

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openhands-ai bot commented Feb 11, 2026

I'm on it! neubig can track my progress at all-hands.dev

Update test to expect temperature=None instead of 0.0, aligning with
the PR's change to get_default_temperature() returning None by default.

Co-authored-by: openhands <openhands@all-hands.dev>
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openhands-ai bot commented Feb 11, 2026

Summary

I've successfully addressed the failing CI for PR #1989 by:

Completed Tasks:

  1. Checked the failing CI - Identified that the sdk-tests job was failing with test_llm_config_defaults expecting temperature == 0.0 but getting None

  2. Merged main - Merged origin/main into the fix-default-temperature-to-none branch to incorporate the latest changes

  3. Reproduced locally - Ran the failing test locally and confirmed the issue

  4. Fixed the issue - Updated tests/sdk/config/test_llm_config.py to expect temperature is None instead of temperature == 0.0, aligning with the PR's intended change to get_default_temperature() returning None by default

Change Made:

-    assert config.temperature == 0.0
+    assert config.temperature is None  # None to use provider defaults

Verification:

  • All 15 tests in test_llm_config.py pass
  • All 130 tests in test_model_features.py pass

Pushed:

The fix has been pushed to the fix-default-temperature-to-none branch. The CI should now pass.

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github-actions bot commented Feb 11, 2026

Coverage

Coverage Report •
FileStmtsMissCoverMissing
openhands-sdk/openhands/sdk/llm
   llm.py4657883%422, 475, 696, 802, 804–805, 833, 883, 894–896, 900–904, 912–914, 924–926, 929–930, 934, 936–937, 939, 1097, 1102–1103, 1300–1301, 1310, 1323, 1325–1330, 1332–1349, 1352–1356, 1358–1359, 1365–1374, 1425, 1427
openhands-sdk/openhands/sdk/llm/utils
   model_features.py40197%32
TOTAL18281556969% 

@neubig neubig marked this pull request as ready for review February 11, 2026 01:19
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🟡 Taste Rating: Acceptable

Pragmatic fix to a real problem, but breaks existing behavior without proper user migration guidance.

The core change is simple and solves the claude-4.6 incompatibility issue. However, this is a significant behavior change that moves from deterministic outputs (temp=0.0) to provider-dependent defaults. See inline comments for specific concerns.

VERDICT: ✅ Worth merging after addressing migration documentation

KEY INSIGHT: This is the right technical fix, but users who relied on deterministic behavior need explicit guidance on setting temperature=0.0 in their configs.

enyst and others added 4 commits February 11, 2026 03:10
Co-authored-by: openhands <openhands@all-hands.dev>
Co-authored-by: openhands <openhands@all-hands.dev>
Co-authored-by: openhands <openhands@all-hands.dev>
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Thank you for this! I think maybe we can then remove the DEFAULT_TEMPERATURE_MODELS too? That’s there because Kimi is a reasoning model that doesn’t accept effort, if I recall correctly, but it needs temperature 1 like reasoning models.

I had the agent test Kimi:

  • for 2.5, it worked fine with None
  • for 2-thinking, no deployments found. (maybe it’s legacy now; we may want to remove it from eval proxy, since it doesn’t appear to work anymore)

Please see PR:

openhands-agent and others added 6 commits February 11, 2026 15:36
Addresses review comment asking for more explicit documentation about:
- What None means (provider default)
- How to get deterministic behavior (explicitly set 0.0)
- The typical temperature range

Co-authored-by: openhands <openhands@all-hands.dev>
Co-authored-by: OpenHands Bot <contact@all-hands.dev>
As per enyst's suggestion on PR #1989:
- Remove DEFAULT_TEMPERATURE_MODELS entirely
- get_default_temperature() now returns None for all models
- This simplifies the codebase and lets all models use their provider's default temperature
- Previously Kimi 2.5 was tested to work fine with None

Co-authored-by: openhands <openhands@all-hands.dev>
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enyst commented Feb 11, 2026

FWIW, PR 1994 is a PR to this PR. 😅

@neubig neubig added the review-this This label triggers a PR review by OpenHands label Feb 12, 2026 — with OpenHands AI
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🟡 Taste Rating: Acceptable - Solves a real problem with elegant simplification, but introduces a breaking change that needs careful consideration.

Verdict: Worth merging with minor improvements to address backward compatibility concerns and design consistency.

Key Insight: This trades deterministic defaults for provider flexibility—a pragmatic choice, but one that changes behavior for all existing users.

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🔴 Taste Rating: Needs Rework

This PR simplifies the code (good!) but introduces a breaking change that violates the "never break userspace" principle. Users relying on deterministic outputs (temperature=0.0) will now get unpredictable provider defaults.


[CRITICAL ISSUES] - Must Fix

1. Breaking Change Without Documentation

File: openhands-sdk/openhands/sdk/llm/llm.py (lines 180-185)

🔴 Critical: This description doesn't mention that this is a BREAKING CHANGE. Users who relied on temperature=0.0 for deterministic outputs will now get provider-specific defaults (which vary: OpenAI defaults to 1.0, Anthropic to 1.0, etc.).

You've broken userspace without documenting it. At minimum:

  1. Clear migration guide: "To preserve deterministic behavior, explicitly set temperature=0.0"
  2. Deprecation warning in release notes
  3. Consider a compatibility flag for one release cycle

Suggested fix:

temperature: float | None = Field(
    default=None,
    ge=0,
    description=(
        "Sampling temperature for response generation. "
        "Defaults to None (uses provider default, typically 1.0 for most models). "
        "BREAKING CHANGE: Previously defaulted to 0.0 for deterministic outputs. "
        "To restore deterministic behavior, explicitly set temperature=0.0. "
        "Higher values (0.7-1.0) increase creativity and randomness."
    ),
)

2. Unused Parameter - Code Smell

File: openhands-sdk/openhands/sdk/llm/utils/model_features.py (line 183)

🔴 Critical: The _model parameter is now completely ignored (indicated by the underscore prefix). This is a code smell that screams "delete this function entirely."

If the model parameter is never used, why does this function exist? Either:

  1. Make it a module-level constant: DEFAULT_TEMPERATURE = None
  2. Delete it and use None directly where needed
  3. Or explain why we need the indirection

The function signature promises model-specific logic but delivers nothing. That's broken by design.


[IMPROVEMENT OPPORTUNITIES] - Should Fix

3. Misleading Documentation

File: openhands-sdk/openhands/sdk/llm/utils/model_features.py (lines 184-189)

🟠 Important: The docstring says "Return the default temperature for a given model pattern" but the model is completely ignored. This is a lie.

Suggested fix:

def get_default_temperature(_model: str) -> float | None:
    """Return None to allow providers to use their default temperature.
    
    This function exists for backward compatibility and may be removed in future versions.
    To use provider defaults, pass temperature=None when creating LLM instances.
    """
    return None

4. Missing Integration Tests

File: tests/sdk/llm/test_model_features.py (lines 342-346)

🟠 Important: These tests only verify the function returns None. They don't test what matters:

  1. Does passing temperature=None to a provider actually work?
  2. Does it fix the claude-4.6 issue mentioned in #1913?
  3. What temperature does each provider actually use when None is passed?

You're testing the implementation, not the behavior. Add tests that:

  • Verify LiteLLM/providers accept temperature=None
  • Confirm claude-4.6 no longer errors
  • Document what "provider default" means for major providers

VERDICT

Needs rework: The simplification is good in principle, but the breaking change and unused parameter issues must be addressed first.

KEY INSIGHT

Simplifying code by removing special cases is "good taste" - BUT you cannot break existing user expectations in the process. Either preserve backward compatibility with explicit opt-in to new behavior, or clearly document the breaking change and provide a migration path.

As per review comment on PR #1989:
- Remove the unused _model parameter since DEFAULT_TEMPERATURE_MODELS was removed
- Function now returns None without needing model info
- Updated tests to use new function signature

Co-authored-by: openhands <openhands@all-hands.dev>
@enyst enyst added behavior-initiative This is related to the system prompt sections and LLM steering. and removed behavior-initiative This is related to the system prompt sections and LLM steering. labels Feb 14, 2026
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Taste Rating: 🟡 Acceptable

This is pragmatic simplification that solves a real problem (claude-4.6 incompatibility), but has a documentation discrepancy and potential breaking change concerns.

The Good: Eliminates model-specific special cases, defers to provider defaults, and simplifies the codebase. This is the right direction.

Key Issues: PR description claims model-specific logic is preserved but the code removes it entirely. Function signature change may break external callers.

@neubig neubig requested a review from all-hands-bot February 15, 2026 23:23
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Taste Rating: 🟡 Acceptable

The simplification is good and solves a real problem (claude-4.6 errors). However, this is a breaking change that affects all existing users who relied on deterministic outputs. The code is cleaner after this change, but the user impact needs careful consideration.

Address AI review comments:
- Fix docstring to not mention 'for a given model' since function no longer takes model param
- Explicitly document the breaking change from 0.0 to None default
- Add rationale and guidance for users who need deterministic outputs

Co-authored-by: openhands <openhands@all-hands.dev>
@neubig neubig requested a review from all-hands-bot February 15, 2026 23:33
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Taste Rating: 🟡 Acceptable - The simplification is elegant, but there's a critical breaking change concern.

[CRITICAL ISSUES]

The code previously set temperature=1.0 explicitly for kimi-k2-thinking and kimi-k2.5 models. Removing this special case without explanation violates the "Never Break Userspace" principle. Those special cases existed for a reason - were those models incompatible with temperature=0.0? Do they work correctly with None?

[IMPROVEMENT OPPORTUNITIES]

The data structure simplification (removing DEFAULT_TEMPERATURE_MODELS list) is good taste - it eliminates special cases. However, this isn't just a refactor; it's a behavioral change that needs verification.

[TESTING GAPS]

Tests were updated to expect None, but there's no coverage proving that previously special-cased models (kimi-k2-thinking, kimi-k2.5) still work correctly with None instead of 1.0.

VERDICT:Needs verification - Core simplification is sound, but the breaking change for kimi models must be validated before merging.

KEY INSIGHT: You're trading special-case complexity for potential runtime breakage - verify the kimi models work with None before shipping.

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Looks like there are a few issues preventing this PR from being merged!

  • GitHub Actions are failing:
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If you'd like me to help, just leave a comment, like

@OpenHands please fix the failing actions on PR #1989 at branch `fix-default-temperature-to-none`

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enyst commented Feb 16, 2026

The agent missed this:

The code previously set temperature=1.0 explicitly for kimi-k2-thinking and kimi-k2.5 models. Removing this special case without explanation violates the "Never Break Userspace" principle. Those special cases existed for a reason - were those models incompatible with temperature=0.0? Do they work correctly with None?

Yes, I tested it, previous comment #1989 (review) details temperature. In the linked PR, Kimi 2.5 failed because of the similar top_p issue.


On another note, I would love to know if Xingyao is okay with this change, if he saw this issue (and/or slack discussion). Maybe we can give it a moment for potential issues to be clarified, before merging?

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neubig commented Feb 16, 2026

/rerun

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neubig commented Feb 19, 2026

@OpenHands fix failing CI.

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I'm on it! neubig can track my progress at all-hands.dev

…-default-temperature-to-none

This merges enyst's cleanup changes:
- Remove get_default_temperature function entirely
- Add get_default_top_p for Kimi and HuggingFace models
- Centralize top_p defaults for models that need them

Co-authored-by: openhands <openhands@all-hands.dev>
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openhands-ai bot commented Feb 19, 2026

Summary

I investigated the CI status for PR #1989 and found that no code changes were needed - the CI was already in a passing state.

What I Did:

  1. ✅ Checked the current git status - branch fix-default-temperature-to-none was already up to date with origin/fix-default-temperature-to-none
  2. ✅ Monitored the CI checks until all completed
  3. ✅ Verified all checks passed

CI Status:

All 24 required checks passed successfully:

  • Pre-commit checks ✅
  • SDK tests, tools tests, agent-server tests, cross-tests ✅
  • API breakage checks ✅
  • Deprecation deadline checks ✅
  • Review Thread Gate ✅
  • Agent Server builds (golang, java, python for amd64/arm64) ✅
  • Agent Server binary tests (ubuntu/macOS) ✅
  • OpenAPI Schema check ✅

Conclusion:

The failing CI from the previous comment by @neubig had already been fixed in earlier commits. The branch was merged with main and all tests were passing. No additional changes were required - I simply waited for all the CI jobs (including the longer-running Docker image builds) to complete and verified they all passed.

Like temperature, top_p should default to None to let providers use their
own defaults. Only models that require specific values (e.g., Kimi K2.5
needs 0.95) get auto-configured.

Co-authored-by: openhands <openhands@all-hands.dev>
Kimi K2.5 works fine with top_p=None (uses provider default), so we don't
need to special-case it anymore. The override was only needed when top_p
defaulted to 1.0.

Co-authored-by: openhands <openhands@all-hands.dev>
Let HuggingFace use its provider default for top_p rather than forcing 0.9.
This is consistent with letting providers handle their own defaults.

Co-authored-by: openhands <openhands@all-hands.dev>
Remove DEFAULT_TOP_P_MODELS and get_default_top_p function.
All models now use provider defaults for top_p (None).

Co-authored-by: openhands <openhands@all-hands.dev>
Co-authored-by: openhands <openhands@all-hands.dev>
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🟡 Taste Rating: Acceptable - Elegant simplification that solves a real problem, but introduces a second undocumented breaking change.

The Good: Eliminates special-case logic and model-specific mappings. This is the right direction - simpler data structures, fewer edge cases.

Key Concerns: top_p breaking change not mentioned in PR description, and HuggingFace special-case removal needs verification.

"or higher values (0.7-1.0) for more creative responses."
),
)
top_p: float | None = Field(
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🟠 Important - Undocumented Breaking Change: The PR title and description only mention temperature changing to None, but top_p is also changing from 1.0 to None. This is a second breaking change that affects ALL models.

Impact: Users who explicitly relied on top_p=1.0 behavior (OpenAI default) will now get provider-specific defaults, which may differ.

Recommendation: Update the PR description to explicitly call out the top_p change alongside the temperature change.

if d.get("top_p", 1.0) == 1.0:
d["top_p"] = 0.9

return d
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🟠 Important - Special Case Removal: The HuggingFace-specific top_p coercion that was removed above this line existed because "HF doesn't support the OpenAI default value for top_p (1)".

Risk: Now that top_p defaults to None instead of 1.0, HuggingFace models might:

  1. Still reject whatever provider default they receive
  2. Behave unexpectedly if their provider default differs from 0.9

Question: Was this tested with actual HuggingFace models? If the provider now handles None correctly for HF models, this removal is fine. But if not, we're trading one compatibility issue (claude-4.6) for another (HuggingFace).

Recommendation: Either verify HF models work with top_p=None or preserve this special case.

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RFC: Always set temperature to default?

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