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BenchLM
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Model A
Grok 4.20

xAI

67.13/100

Supported · Public rank #31

90% interval 58.5–75.8

Grok 4.20 vs Grok 4 Fast (Reasoning)

Updated September 10, 2026. Public scores include evidence status and uncertainty. They are not guarantees for a specific workload.

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Model B
Grok 4 Fast (Reasoning)

xAI

51.31/100

Supported · Public rank #120

90% interval 34.3–68.3

Decision reading

Grok 4.20 has the higher public score estimate, 67.13 versus 51.31, but the 90% score intervals overlap. Treat that as a lead, not a settled winner.

1 results are shared. Category rows resting on Estimated evidence or different benchmark sets are marked directional and do not name a winner.

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Which one for your work

Recommendations appear only when a shared evidence basis or an explicit operating constraint supports the call. Secondary and unsupported use cases stay disclosed below the initial list.

No workload recommendation clears the current evidence threshold.

Use the matched evidence, workload costs, and sourced specifications below instead of treating a point score as a universal answer.

Show secondary and unsupported calls

  • Coding work

    Code generation, repair, and software-engineering tasks

    Not enough matched evidence

    Grok 4 Fast (Reasoning) is scored on Estimated evidence for coding, so the reading is directional rather than like-for-like.

    Confidence: limited

  • Agentic work

    Tool use, computer use, and multi-step task completion

    Not enough matched evidence

    Grok 4 Fast (Reasoning) is not ranked on the public lane for agentic, so no winner is named for agentic.

    Confidence: limited

  • Long documents

    Prompts that approach the documented context limit

    No clear pick

    The documented context windows are equal.

    Confidence: documented

  • Chat turn cost

    1K fresh input + 500 output tokens

    Not enough matched evidence

    A complete comparable API-rate estimate is not available for both models.

    Confidence: listed-rates

  • Cache-heavy agent loop cost

    200K cached + 20K fresh input + 10K output tokens

    Not enough matched evidence

    A complete comparable API-rate estimate is not available for both models.

    Confidence: rate-fallback

  • Repository review cost

    50K fresh input + 3K output tokens

    Not enough matched evidence

    A complete comparable API-rate estimate is not available for both models.

    Confidence: listed-rates

What is actually comparable

Shared results can support a head-to-head reading. Results present for only one model describe coverage, not superiority.

Shared results
1
Grok 4.20 only
22
Grok 4 Fast (Reasoning) only
0
Like-for-like categories
0 / 8

2 categories rest on Estimated evidence or different evidence sets. Those rows remain visible for coverage context but do not name a winner.

Category results, on a stated basis

Each row shows the public-lane category score for both models: the BenchAlign lane for agentic, coding, and knowledge, and the weighted public rows elsewhere, with the same rank each model page reports. A row is like-for-like only when both scores rest on Supported evidence or the same weighted set. Directional and not-comparable rows remain visible, but they never receive a winner.

Coding

Directional only
Grok 4.20
28.2
Supported · #141/151
Grok 4 Fast (Reasoning)
41.1
Estimated · #110/151
Basis
BenchAlign lane · 6 vs 1 public rows
Reading
Directional only

Knowledge

Directional only
Grok 4.20
49.4
Supported · #85/183
Grok 4 Fast (Reasoning)
47.1
Estimated · #99/183
Basis
BenchAlign lane · 6 vs 0 public rows
Reading
Directional only

Agentic

Not comparable
Grok 4.20
26.7
Supported · #145/152
Grok 4 Fast (Reasoning)
Not ranked
Basis
BenchAlign lane · 4 vs 0 public rows
Reading
Not comparable

Reasoning

Not comparable
Grok 4.20
34.2
Unranked · 2 rankable rows
Grok 4 Fast (Reasoning)
71.7
Unranked · 2 rankable rows
Basis
Provisional lane · 2 vs 0 weighted rows
Reading
Not comparable

Math

Not comparable
Grok 4.20
Not ranked
Grok 4 Fast (Reasoning)
Not ranked
Basis
Provisional lane · 0 vs 0 weighted rows
Reading
Not comparable

Multilingual

Not comparable
Grok 4.20
Not ranked
Grok 4 Fast (Reasoning)
Not ranked
Basis
Provisional lane · 0 vs 0 weighted rows
Reading
Not comparable

Multimodal

Not comparable
Grok 4.20
34.6
#43/48
Grok 4 Fast (Reasoning)
51.1
Unranked · 1 rankable row
Basis
Provisional lane · 2 vs 0 weighted rows
Reading
Not comparable

Instruction following

Not comparable
Grok 4.20
Not ranked
Grok 4 Fast (Reasoning)
60.3
#72/123
Basis
Provisional lane · 0 vs 0 weighted rows
Reading
Not comparable

Ranks count the models scored in each category’s lane, so the agentic, coding, and knowledge denominators (BenchAlign) differ from the provisional-lane categories. Unranked scores sit on the lane’s scale but never name a winner. Like-for-like rows within 0.5 points read as a practical tie.

Shape of the matched evidence

Only shared public evidence is shown. Sparse evidence stays a ruled list rather than being closed into a radar shape.

A shared-evidence shape is not available.

BenchLM does not draw a radar or infer missing axes when the matched evidence is too sparse.

What each workload costs

Three fixed token mixes turn per-token rates into comparable decisions. Each scenario states context fit and whether cached input had to fall back to the published list-input rate.

Chat turn

1K fresh input + 500 output tokens

Grok 4.20
$0.005
Fits in one request
Grok 4 Fast (Reasoning)
API rate not published
Fits in one request

Grok 4 Fast (Reasoning) has no comparable published API token rate.

Repository review

50K fresh input + 3K output tokens

Grok 4.20
$0.118
Fits in one request
Grok 4 Fast (Reasoning)
API rate not published
Fits in one request

Grok 4 Fast (Reasoning) has no comparable published API token rate.

Cache-heavy agent loop

200K cached + 20K fresh input + 10K output tokens

Grok 4.20
$0.5
Fits in one request
Cached input priced at the published list-input rate
Grok 4 Fast (Reasoning)
API rate not published
Fits in one request
Cached-input rate unavailable

Grok 4.20 has no published cached-input rate, so cached tokens use its listed input rate. Grok 4 Fast (Reasoning) has no comparable published API token rate.

Specification differences

Sourced differences are shown directly. Missing facts stay explicit instead of being inferred from a model name or family.

Context window

Maximum documented context; output-token limits may be lower.

Grok 4.20

2M

Grok 4 Fast (Reasoning)

2M

API model ID

Grok 4.20

Not sourced

Grok 4 Fast (Reasoning)

Not sourced

Cached-input rate

A missing cached-input rate falls back to the listed input rate only in the stated workload estimate.

Grok 4.20

Not published

Grok 4 Fast (Reasoning)

No comparable hosted API rate

Documented inputs

Grok 4.20

Not sourced

Grok 4 Fast (Reasoning)

Not sourced

Documented outputs

Grok 4.20

Not sourced

Grok 4 Fast (Reasoning)

Not sourced

Provider availability

Grok 4.20

Not sourced

Grok 4 Fast (Reasoning)

Not sourced

Reasoning profile

Grok 4.20

Reasoning

Grok 4 Fast (Reasoning)

Reasoning

Weight access

Grok 4.20

Proprietary

Grok 4 Fast (Reasoning)

Proprietary

License

Grok 4.20

Proprietary

Grok 4 Fast (Reasoning)

Proprietary

Release date

Grok 4.20

2026-03-10

Grok 4 Fast (Reasoning)

2025-09-19

If you already use one of these models
Deployment change
Both entries list xAI as the provider. Confirm endpoint, model ID, limits, and feature support before switching.
Quality signal
Grok 4.20 has the higher public score estimate, 67.13 versus 51.31, but the 90% score intervals overlap.
Workload cost
A complete comparable API-rate estimate is not available for both models.
Context tradeoff
Both models list 2M.

Run the same representative tasks against both endpoints before changing production traffic.

Benchmark evidence

The full public result ledger is available for audit without forcing a wide desktop table onto a phone.

Browse raw public benchmark evidence23 rows

Agentic

  • Terminal-Bench 2.0

    Grok 4.2047.1%
    Source
    Grok 4 Fast (Reasoning)—

    Not directly comparable

  • DeepSearchQA

    Grok 4.2062.8%
    Source
    Grok 4 Fast (Reasoning)—

    Not directly comparable

  • Gert Labs

    Grok 4.2038.36%
    Source
    Grok 4 Fast (Reasoning)—

    Not directly comparable

  • Terminal-Bench 2.1 (Vals)

    Grok 4.2044.2%
    Source
    Grok 4 Fast (Reasoning)—

    Not directly comparable

Coding

  • LiveCodeBench Pro

    Grok 4.2074.2%
    Source
    Grok 4 Fast (Reasoning)—

    Not directly comparable

  • SWE-bench Verified

    Grok 4.2076.7%
    Source
    Grok 4 Fast (Reasoning)—

    Not directly comparable

  • SWE-bench Pro

    Grok 4.2051.8%
    Source
    Grok 4 Fast (Reasoning)—

    Not directly comparable

  • Vibe Code Bench

    Shared source
    Grok 4.204.06%
    Grok 4 Fast (Reasoning)0.00%

    Grok 4.20 leads this result

  • LiveCodeBench (Vals)

    Grok 4.2084.3%
    Source
    Grok 4 Fast (Reasoning)—

    Not directly comparable

  • SWE-bench (Vals)

    Grok 4.2072.2%
    Source
    Grok 4 Fast (Reasoning)—

    Not directly comparable

Reasoning

  • ARC-AGI-2

    Grok 4.2053.3%
    Source
    Grok 4 Fast (Reasoning)—

    Not directly comparable

  • ARC-AGI-3

    Grok 4.200.1%
    Source
    Grok 4 Fast (Reasoning)—

    Not directly comparable

Knowledge

  • GPQA-D

    Grok 4.2088.5%
    Source
    Grok 4 Fast (Reasoning)—

    Not directly comparable

  • HLE w/o tools

    Grok 4.2031.6%
    Source
    Grok 4 Fast (Reasoning)—

    Not directly comparable

  • HealthBench Hard

    Grok 4.2020.3%
    Source
    Grok 4 Fast (Reasoning)—

    Not directly comparable

  • MedXpertQA (Text)

    Grok 4.2050.2%
    Source
    Grok 4 Fast (Reasoning)—

    Not directly comparable

  • GPQA Diamond (Vals)

    Grok 4.2088.6%
    Source
    Grok 4 Fast (Reasoning)—

    Not directly comparable

  • MMLU-Pro (Vals)

    Grok 4.2086.3%
    Source
    Grok 4 Fast (Reasoning)—

    Not directly comparable

Multimodal

  • MMMU-Pro

    Grok 4.2075.2%
    Source
    Grok 4 Fast (Reasoning)—

    Not directly comparable

  • CharXiv

    Grok 4.2060.9%
    Source
    Grok 4 Fast (Reasoning)—

    Not directly comparable

  • ERQA

    Grok 4.2054.1%
    Source
    Grok 4 Fast (Reasoning)—

    Not directly comparable

  • SimpleVQA

    Grok 4.2057.4%
    Source
    Grok 4 Fast (Reasoning)—

    Not directly comparable

  • MedXpertQA (MM)

    Grok 4.2065.8%
    Source
    Grok 4 Fast (Reasoning)—

    Not directly comparable

Frequently asked questions

Which is better, Grok 4.20 or Grok 4 Fast (Reasoning)?

Grok 4.20 has the higher public score estimate, 67.13 versus 51.31, but the 90% score intervals overlap. The higher estimate is not a decisive winner because the uncertainty ranges overlap.

Which is better for coding, Grok 4.20 or Grok 4 Fast (Reasoning)?

Grok 4 Fast (Reasoning) scores higher for coding on the public lane, 41.1 to 28.2. Grok 4 Fast (Reasoning) is scored on Estimated evidence for coding, so the reading is directional rather than like-for-like. BenchLM does not name a winner for coding from a directional reading; read the shared benchmark rows directly and test the models on the same task set.

Which is better for agentic tasks, Grok 4.20 or Grok 4 Fast (Reasoning)?

Grok 4 Fast (Reasoning) is not ranked on the public lane for agentic tasks, so no winner is named for agentic tasks.

Which costs less, Grok 4.20 or Grok 4 Fast (Reasoning)?

Both models do not have comparable published API token rates, so this page does not name a universal price winner.

Which has the larger context window, Grok 4.20 or Grok 4 Fast (Reasoning)?

Both models list the same context window, 2M.

Related comparisons

Compare API pricing Read the methodology Open the model selector

Last updated September 10, 2026

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