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Grok 4.1 Fast Reasoning
xaixai/grok-4-1-fast-reasoning
How TheRouter serves this differently from the vendor
As the vendor operates it
xAI retired the upstream grok-4-1-fast-reasoning slug on May 15, 2026 and redirects it to grok-4.3; the vendor does not present it as a current standalone model with a separate model card.
On TheRouter
TheRouter still exposes the listed xai/grok-4-1-fast-reasoning model id through its OpenAI-compatible chat route with TheRouter catalog pricing and a 2M context configuration, so customers should treat it as a compatibility route and validate before migrating.
API guide
Reasoning chat
Use the OpenAI-compatible chat completions endpoint with the TheRouter model id. Keep this snippet for compatibility tests; prefer successor models for new builds.
cURL
curl https://api.therouter.ai/v1/chat/completions \
-H "Authorization: Bearer $THEROUTER_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"model": "xai/grok-4-1-fast-reasoning",
"messages": [
{"role": "system", "content": "Reason carefully and flag uncertainty."},
{"role": "user", "content": "Summarize the migration risks in this plan."}
],
"reasoning": {"effort": "medium"}
}'Reasoning + tool calls
The model row supports tools and tool_choice. Use narrow schemas so legacy compatibility tests measure the route, not schema bloat.
cURL
curl https://api.therouter.ai/v1/chat/completions \
-H "Authorization: Bearer $THEROUTER_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"model": "xai/grok-4-1-fast-reasoning",
"messages": [{"role": "user", "content": "Check order ord_123 and decide whether to escalate."}],
"tools": [{"type": "function", "function": {"name": "get_order_status", "description": "Return order status by id", "parameters": {"type": "object", "properties": {"order_id": {"type": "string"}}, "required": ["order_id"]}}}],
"tool_choice": "auto",
"reasoning": {"effort": "low"}
}'Fact ledger — every claim on this page traces here
| source | URL | retrieved | |
|---|---|---|---|
| TheRouter model ID | — | — | verified |
| Upstream slug status | docs.x.ai ↗ | 2026-08-08 | verified |
| Context window | — | — | verified |
| Input modalities | — | — | verified |
| Output modalities | — | — | verified |
| TheRouter pricing | — | — | verified |
| Reasoning parameter | docs.x.ai ↗ | 2026-08-08 | verified |
| Structured outputs | — | — | verified |
| Training cutoff | — | — | unknown |
| License | — | — | verified |
| Exact retired slug benchmarks | docs.x.ai ↗ | 2026-08-08 | unknown |
| Successor benchmark guidance | docs.x.ai ↗ | 2026-08-08 | unknown |
| TheRouter route validation | docs.x.ai ↗ | 2026-08-08 | unknown |
| xAI retires Grok 4.1 fast slugs and redirects them to Grok 4.3 | docs.x.ai ↗ | 2026-08-08 | verified |
| Is xai/grok-4-1-fast-reasoning the same as Grok 4.3? | docs.x.ai ↗ | 2026-08-08 | to verify |
| Should I use this model for a new production integration? | docs.x.ai ↗ | 2026-08-08 | to verify |
| Why does the page not list exact benchmark scores? | docs.x.ai ↗ | 2026-08-08 | to verify |