diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index 1e8d09b0da..d8231e0197 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -29,6 +29,9 @@ Fixed
 
 * Fixed eventlet monkey patching so more of the unit tests work under pytest. #5689
 
+* Fix and reenable prance-based openapi spec validation, but make our custom ``x-api-model`` validation optional as the spec is out-of-date. #5709
+  Contributed by @cognifloyd
+
 Added
 ~~~~~
 
diff --git a/st2common/st2common/cmd/validate_api_spec.py b/st2common/st2common/cmd/validate_api_spec.py
index 01659be732..0a9facd9c1 100644
--- a/st2common/st2common/cmd/validate_api_spec.py
+++ b/st2common/st2common/cmd/validate_api_spec.py
@@ -22,8 +22,8 @@
 from __future__ import absolute_import
 import os
 
+import prance
 from oslo_config import cfg
-from prance import ResolvingParser
 
 from st2common import config
 from st2common import log as logging
@@ -45,6 +45,14 @@
     )
 )
 
+# When disabled, only load the spec in prance to validate. Otherwise check for x-api-model as well.
+# validate-defs is disabled by default until these are resolved:
+#   https://github.com/StackStorm/st2/issues/3575
+#   https://github.com/StackStorm/st2/issues/3788
+cfg.CONF.register_cli_opt(
+    cfg.BoolOpt("validate-defs", short="-d", required=False, default=False)
+)
+
 cfg.CONF.register_cli_opt(
     cfg.BoolOpt("generate", short="-c", required=False, default=False)
 )
@@ -71,6 +79,7 @@ def _validate_definitions(spec):
 
             if verbose:
                 LOG.info("Supplied definition for model %s: \n\n%s.", model, definition)
+                msg += "\n"
 
             error = True
             LOG.error(msg)
@@ -81,6 +90,7 @@ def _validate_definitions(spec):
 def validate_spec():
     spec_file = cfg.CONF.spec_file
     generate_spec = cfg.CONF.generate
+    validate_defs = cfg.CONF.validate_defs
 
     if not os.path.exists(spec_file) and not generate_spec:
         msg = (
@@ -100,13 +110,16 @@ def validate_spec():
             f.write(spec_string)
             f.flush()
 
-    parser = ResolvingParser(spec_file)
+    parser = prance.ResolvingParser(spec_file)
     spec = parser.specification
 
+    if not validate_defs:
+        return True
+
     return _validate_definitions(spec)
 
 
-def teartown():
+def teardown():
     common_teardown()
 
 
@@ -118,11 +131,14 @@ def main():
         # The spec loader do not allow duplicate keys.
         spec_loader.load_spec("st2common", "openapi.yaml.j2")
 
-        ret = 0
+        # run the schema through prance to validate openapi spec.
+        passed = validate_spec()
+
+        ret = 0 if passed else 1
     except Exception:
         LOG.error("Failed to validate openapi.yaml file", exc_info=True)
         ret = 1
     finally:
-        teartown()
+        teardown()
 
     return ret
diff --git a/st2common/st2common/models/api/pack.py b/st2common/st2common/models/api/pack.py
index 6de2893427..8c31718b0e 100644
--- a/st2common/st2common/models/api/pack.py
+++ b/st2common/st2common/models/api/pack.py
@@ -383,12 +383,17 @@ class PackInstallRequestAPI(BaseAPI):
     schema = {
         "type": "object",
         "properties": {
-            "packs": {"type": "array"},
+            "packs": {"type": "array"},  # TODO: add enum
             "force": {
                 "type": "boolean",
                 "description": "Force pack installation",
                 "default": False,
             },
+            "skip_dependencies": {
+                "type": "boolean",
+                "description": "Set to True to skip pack dependency installations.",
+                "default": False,
+            },
         },
     }
 
diff --git a/st2common/st2common/openapi.yaml b/st2common/st2common/openapi.yaml
index 107b97a1c2..e86e42727d 100644
--- a/st2common/st2common/openapi.yaml
+++ b/st2common/st2common/openapi.yaml
@@ -1998,7 +1998,7 @@ paths:
           schema:
             type: array
             items:
-              $ref: '#/definitions/PackView'
+              $ref: '#/definitions/DataFilesSubSchema'
           examples:
             application/json:
               ref: 'core.local'
@@ -2391,7 +2391,7 @@ paths:
           description: User performing the operation.
       responses:
         '200':
-          description: Policy created successfully.
+          description: Policy list
           schema:
             type: array
             items:
@@ -3074,7 +3074,7 @@ paths:
           description: User performing the operation.
       responses:
         '200':
-          description: List of rules
+          description: List of runner types
           schema:
             type: array
             items:
@@ -4883,7 +4883,7 @@ definitions:
         type: object
         description: Execution result
         properties:
-          $ref: '#/definitions/Execution'
+          $ref: '#/definitions/Execution/properties'
       message:
         type: string
   AliasMatchAndExecuteInputAPI:
@@ -5172,8 +5172,9 @@ definitions:
       skip_dependencies:
         type: boolean
         description: Set to True to skip pack dependency installations.
-        required: false
         default: false
+    required:
+      - packs
   PacksUninstall:
     type: object
     properties:
@@ -5198,6 +5199,10 @@ definitions:
         type: array
         items:
           $ref: '#/definitions/PacksContentRegisterType'
+      fail_on_failure:
+        type: boolean
+        description: True to fail on failure
+        default: true
   PacksContentRegisterType:
           type: string
           enum: ['all',
diff --git a/st2common/st2common/openapi.yaml.j2 b/st2common/st2common/openapi.yaml.j2
index a54bb423f1..f053f0f3d0 100644
--- a/st2common/st2common/openapi.yaml.j2
+++ b/st2common/st2common/openapi.yaml.j2
@@ -1994,7 +1994,7 @@ paths:
           schema:
             type: array
             items:
-              $ref: '#/definitions/PackView'
+              $ref: '#/definitions/DataFilesSubSchema'
           examples:
             application/json:
               ref: 'core.local'
@@ -2387,7 +2387,7 @@ paths:
           description: User performing the operation.
       responses:
         '200':
-          description: Policy created successfully.
+          description: Policy list
           schema:
             type: array
             items:
@@ -3070,7 +3070,7 @@ paths:
           description: User performing the operation.
       responses:
         '200':
-          description: List of rules
+          description: List of runner types
           schema:
             type: array
             items:
@@ -4879,7 +4879,7 @@ definitions:
         type: object
         description: Execution result
         properties:
-          $ref: '#/definitions/Execution'
+          $ref: '#/definitions/Execution/properties'
       message:
         type: string
   AliasMatchAndExecuteInputAPI:
@@ -5168,8 +5168,9 @@ definitions:
       skip_dependencies:
         type: boolean
         description: Set to True to skip pack dependency installations.
-        required: false
         default: false
+    required:
+      - packs
   PacksUninstall:
     type: object
     properties:
@@ -5194,6 +5195,10 @@ definitions:
         type: array
         items:
           $ref: '#/definitions/PacksContentRegisterType'
+      fail_on_failure:
+        type: boolean
+        description: True to fail on failure
+        default: true
   PacksContentRegisterType:
           type: string
           enum: ['all',