Claude Opus 4.1 deprecated, retires August 5, 2026; sampler params return 400 on new models
claude-opus-4-1-20250805 was deprecated June 5, 2026 and retires August 5, 2026 (replacement: claude-opus-4-8); claude-mythos-preview retired June 30, 2026 in favor of claude-mythos-5. Separately, temperature/top_p/top_k return a 400 error when set to non-default values on Opus 4.7+, Opus 4.8, and Sonnet 5.
Deadline: 2026-08-05
Action note
Audit API usage for claude-opus-4-1-20250805 and mythos-preview calls, migrate to claude-opus-4-8 / claude-mythos-5 before 2026-08-05, and strip non-default temperature/top_p/top_k from requests to newer models.
Claude Fable 5 / Mythos 5 use new tokenizer: ~30% more tokens for the same text
Claude Fable 5 and Mythos 5 use the tokenizer introduced with Opus 4.7, which produces roughly 30% more tokens than earlier models for the same text, and billing reflects the higher counts. Token counts measured on older models must not be reused; the free count_tokens endpoint returns counts for the model you pass.
Action note
Before migrating any workload to Fable 5 or Mythos 5, recount your prompts via /v1/messages/count_tokens with the target model and re-budget costs and context-window fit for the ~30% token increase.
New read-only Admin API endpoints (GET /v1/organizations/rate_limits and per-workspace variants) return configured limits per rate-limit group with values like requests_per_minute and input/output tokens per minute. Requires an Admin API key; limits can be read but not updated via the API.
Action note
Replace hardcoded rate-limit values in gateways and proxies with a scheduled fetch of /v1/organizations/rate_limits, and pair it with the Usage API for limit-utilization alerting.
Usage & Cost Admin API adds geo, context-window, and fast-mode reporting dimensions
Admin-key endpoints /v1/organizations/usage_report/messages and /v1/organizations/cost_report report token usage (1m/1h/1d buckets, groupable by api_key, workspace, model, service_tier, context_window, inference_geo) and daily USD costs. Data lands within about 5 minutes; not available on Claude Platform on AWS.
Action note
Build cost-reconciliation and per-workspace chargeback jobs against usage_report/messages and cost_report with an Admin API key.