Claude Fable 5 vs Claude Sonnet 5: API Behavior Test
On 2026-07-03, both claude-fable-5 and claude-sonnet-5 appeared in Crazyrouter /v1/models with OpenAI-compatible endpoint support.
Test base URL:
https://cn.crazyrouter.com/v1
Simple exact-output test:
| Model | Response ID | Visible output |
|---|---|---|
claude-fable-5 |
msg_01MPuZqzZwj6ysEuzamkxdUC |
Claude Fable 5 test OK |
claude-sonnet-5 |
msg_0195uVQqkDHcxNFgnJYiPTNV |
Claude Sonnet 5 test OK |
Same JSON task:
| Model | Response ID | Result |
|---|---|---|
claude-fable-5 |
msg_018ht1NoiLUSdhnSAw7ScQ8g |
Returned visible compact JSON |
claude-sonnet-5 |
chatcompl_01VV1nUDJdqUwjgH2zBfVUp7 |
HTTP 200, finish_reason stop, but empty visible content |
Production lesson: validate visible content and output shape. HTTP 200 is not enough.