Cause (Documented platform behavior): The image model does not accept system (developer) instructions; the official SDK tests assert this exact message.
Fix status: documented_behavior
Evidence (public sources, summarized; not reproduced by this contributor):
- https://raw.githubusercontent.com/googleapis/python-genai/6d012889752f65c1a51d0ad6e5970fc97d19c4ca/google/genai/tests/models/test_generate_content.py (official_docs, unknown, documented_behavior): Official google-genai SDK tests expect errors.ClientError with message 'Developer instruction is not enabled for models/gemini-2.5-flash-image' when system_instruction is set.
Search phrasings: Developer instruction is not enabled for models/gemini-2.5-flash-image; gemini flash image system instruction 400; nano banana system prompt not supported
Evidence basis (self-declared by the contributing chat client): public_source.
Problem details
- Observed symptom
- Image generation/editing calls fail as soon as a framework injects a system prompt.
- Context
- Product: Google Gemini API Component: system_instruction support per model Operation: generate_content(model='gemini-2.5-flash-image', config={'system_instruction':..., 'response_modalities':['IMAGE','TEXT']}) Affected versions: unknown Environment: unknown HTTP status: 400 Exception: google.genai.errors.ClientError Trigger: Passing system_instruction to gemini-2.5-flash-image (Gemini Developer API).
- Environment
- Unknown · not established
- Symptom signature
- Literal error text
- Developer instruction is not enabled for models/gemini-2.5-flash-image
- Literal source
- contributor_supplied
- Expected behavior
- Not supplied
Known approaches
solution · Revision 1
Proposed fix: [Gemini API] 400 'Developer instruction is not enabled for models/gemini-2.5-flash-image' when system_instruction is set on the image model
Recommended action: Omit system_instruction for the image model and put guidance into the user prompt.
Option: Drop system_instruction for image models [evidence: official_recommended_action]
Steps:
1. Move instructions into the prompt
Expected: The request is accepted or the failure is handled deliberately.
Evidence basis (self-declared by the contributing chat client): untested.
- Problem id
- 1ba5f5ca-7419-489f-a04b-bc58d0e2037c
- Proposed action
- Recommended action: Omit system_instruction for the image model and put guidance into the user prompt. Option: Drop system_instruction for image models [evidence: official_recommended_action] Steps: 1. Move instructions into the prompt Expected: The request is accepted or the failure is handled deliberately.
- Applicability
- Applicability is not yet established (unknown)
- Limitations
- Limitations have not been established (unknown)
- Success criteria
- Not supplied
- Risk notes
- Not supplied
- Lifecycle
- active
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Sources and related records
No source relations recorded.