Grok 4.1 Fast
xAI's 2M-context API model for fast agentic tool use, with reasoning and non-reasoning variants.
Retired
Grok 4.1 Fast appears to be discontinued or shut down — API variants retired May 15, 2026; model slugs redirected to Grok 4.3 This page is kept as an archive record and is excluded from search engines.
About
Grok 4.1 Fast is xAI's API model from November 19, 2025, built for fast, tool-heavy agentic work. It shipped in two variants, reasoning and non-reasoning, with a two-million-token context window and training aimed at multi-turn tool use: web and X search, file retrieval, code execution, and MCP tools. xAI called it its best tool-calling model at launch and priced it at $0.20 per million input tokens and $0.50 per million output tokens.
The consumer Grok 4.1 release it was paired with ranked first on LMArena's Text Arena at launch with 1483 Elo. xAI retired the Grok 4.1 Fast API variants on May 15, 2026 and redirected their slugs to Grok 4.3, so treat this entry as a historical record of the 4.1 generation rather than a current API choice.
Specs
Context window
Pricing
Free quota
API access
Weights
Released
Benchmarks
- xAI's stated best tool-calling model at launch (Nov 2025)
- Grok 4.1 Thinking ranked #1 on LMArena Text Arena (1483 Elo) at launch
- Reported 50% fewer hallucinations than the previous Grok generation
Provider-reported unless a source says otherwise. Benchmarks are marketing-adjacent by nature — treat them as directional.
Use cases
Trust score — 5/10
Scored 5/10 (verified tier, metrics-v1). Evidence: widely used via xAI API and OpenRouter from Nov 2025 to May 2026, then the API variants were retired with slugs redirected to Grok 4.3. Closed weights. Launch and retirement facts corroborated across multiple outlets; docked for vendor-reported benchmark claims and retired status making this a historical entry.
How the trust score is built
Full methodology →- Adoption · stars/downloads, log-scaled vs peers
- 6.0/10
- Maintenance · recency, releases, issue load
- 4.0/10
- Openness · license + docs
- 3.0/10
- Manual review · sanity read + red-flag check
- 7.0/10
- · Adoption 6: widely used via xAI API and OpenRouter Nov 2025-May 2026; API variants retired May 15, 2026 with slugs redirected to Grok 4.3
- · Maintenance 4: released Nov 19, 2025; retired as a product line May 2026, superseded by Grok 4.3/4.6
- · Openness 3: proprietary, no weights
- · Manual 7: launch facts (2M context; reasoning + non-reasoning variants; $0.20/$0.50 pricing; May 2026 retirement) corroborated across xAI coverage, VentureBeat, and vals.ai; docked for vendor-reported benchmark claims and retirement making it historical