Grok 4.5 vs Claude Opus 5: cost per task is the real scoreboard
Two models landed in the same month with opposite pitches.
Grok 4.5 (xAI, ~Jul 8) is the cheap agent workhorse.
Claude Opus 5 (Anthropic, Jul 24) is near-Fable intelligence at Opus list price.
This brief maps API pricing, independent cost-per-task numbers, benchmarks, and what people actually said over the last 30 days.
Official API rates (short context). Grok doubles when the prompt hits ≥200k tokens.
Opus 5 keeps the Opus-family rate and adds effort knobs (low → max) plus a Fast mode at 2× price.
Grok 4.5 · xAI
$2 / $6500k contexteffort: low/med/high
Input $2.00 / 1M · cached $0.30
Output $6.00 / 1M
≥200k prompt: $4 / $12 (all tokens in request)
In Grok Build, Cursor, xAI console (EU access limited)
Claude Opus 5 · Anthropic
$5 / $251M contexteffort: low→max
Input $5.00 / 1M · cache hit $0.50
Output $25.00 / 1M
Same list price as Opus 4.8; Fast mode ≈ 2× base
Default on Claude Max; API id claude-opus-5
Input ratio
2.5×
Opus costs more per 1M in
Output ratio
4.2×
Opus costs more per 1M out
Grok AA $/task
$0.31
Intelligence Index
Opus 5 AA $/task
$2.03
Intelligence Index (max)
Why output ratio dominates agent bills.
Coding agents emit far more output (and reasoning) tokens than input. A 4.2× gap on output, stacked with Grok’s lower token counts per task, is why community math keeps landing on “Grok is dramatically cheaper per solved ticket,” even when quality is close rather than identical.
2. Cost per task (the metric that matters)
List price is the menu. Cost per task is the receipt. Independent Artificial Analysis runs (and xAI’s own SWE-Bench Pro token stats) show Grok’s edge is price × tokens used, not price alone.
Artificial Analysis — cost per Intelligence Index task
Grok 4.5
$0.31
Opus 4.8 (max)
$1.80
Opus 5 (max)
$2.03
Fable 5
$2.75
Approximate AA published costs. Opus 5 (max) ≈ $2.03/task with higher intelligence than Fable’s $2.75 path; Grok remains the cheap near-frontier point (~6.5× under Opus 5 max on this axis).
Coding-agent cost (Grok Build vs peers)
On AA’s Coding Agent Index (DeepSWE + Terminal-Bench v2 + SWE-Atlas QnA), Grok 4.5 inside Grok Build landed around
$2.49–$2.59 per task with ~1.9M average tokens/task — vs roughly
$11.80 for Fable 5 in Claude Code and $5.07 for GPT-5.5 in Codex (AA article, Jul 8).
That is the “17× under Opus-class” style headline you saw in secondary writeups: not magic, just low rates + fewer tokens.
Axis
Grok 4.5
Opus 5
Read as
API in / out ($/1M)
$2 / $6
$5 / $25
Grok cheaper on paper
AA Intel Index score
~54
~61 (max)
Opus smarter
AA $/Intel-Index task
~$0.31
~$2.03
Grok ~6.5× cheaper
SWE-Bench Pro (vendor-era)
64.7%
see note
Opus 4.8 max was 69.2%; Opus 5 is newer / higher on many agent benches
Terminal-Bench 2.1
83.3%
~89% max
Opus edges TB at max effort
Token thrift (agents)
very high
effort-dependent
xAI: ~4.2× fewer out tokens vs Opus 4.8 max on SWE-Pro
SWE-Pro / TB rows for Opus 5 are still settling on public leaderboards on launch day. Prefer AA + your harness over any single vendor chart.
Opus 5’s real story is “Fable-class work at Opus list price,” not “cheaper than Grok.”
Anthropic and AA both frame Opus 5 as near Fable 5 intelligence at about half Fable’s cost-per-task. That beats Fable and often Opus 4.8 on value. It does not undercut Grok 4.5 on raw $/task for high-volume agent loops.
3. Performance map
Neither model “wins every chart.” Grok’s release pitch was balance + thrift: competitive coding scores without topping Fable/GPT-5.5/Opus on most leaderboards.
Opus 5’s launch pitch is the opposite: new SOTA on several agentic knowledge-work and software evals while staying on the $5/$25 Opus SKU.
Where Grok 4.5 is strong
Terminal / agent coding efficiency — TB 2.1 ~83.3%; SWE Marathon resolution claimed lead in xAI materials; long multi-hour coding loops where token burn compounds.
Cost-constrained Cursor / Grok Build workflows — “Opus-ish quality, faster/cheaper” is the repeated YouTube TL;DR.
Token-efficient execution model in multi-model stacks (replace Sonnet-class workers while keeping a heavier planner).
Where Opus 5 is strong
Intelligence ceiling — AA Index ~61 at max; GDPval-AA v2 and AA-Briefcase leadership on launch coverage.
Hard debugging / root-cause / judgment — early-access quotes (Cursor, Devin, finance, legal) stress thoroughness and self-verification.
Knowledge work + computer use — Anthropic highlights OSWorld, AutomationBench, ARC-AGI 3, and visual artifact quality.
Effort dial — low effort can be cheaper than max while still competitive; max is for the hard path.
“If you want a TL;DR, basically, if you've ever wanted Opus 4.8 quality, but faster and cheaper, that's more or less Grok 4.5.”
YouTube explainers in the last-30-days corpus (pre–Opus 5 launch)
4. What people said (last 30 days)
Pulse from a multi-source pass (Reddit, HN, YouTube, Digg, Techmeme, arXiv, Polymarket; X not fully authed this run).
18 Reddit threads · 17 HN stories · 14 YouTube videos in the comparison corpus.
Grok 4.5 thread
HN launch discussion heavy (700+ pts class threads on xAI’s post).
r/cursor split: some “same as Opus 4.8, cheaper”; some “finishes early / needs more review.”
Common workflow: architect on Opus, code on Grok.
Price/perf praise is louder than pure quality praise.
Opus 5 launch day
HN front page: Anthropic post ~1,200+ pts / hundreds of comments within hours.
r/ClaudeCode “Opus 5 just dropped” quickly into the hundreds of upvotes.
YouTube: “half the price of Fable,” head-to-heads vs Fable, not yet deep Grok bake-offs.
Early note: same $5/$25 as 4.8; value claim is performance-up, not price-down.
“I'm seeing nothing but decent results with Grok 4.5. Same output as Opus 4.8 and a lot cheaper. I'm mostly doing desktop and website dev work.”
r/cursor · community comment in last-30-days sample
“I find grok 4.5 slight worse than opus 4.8… finish early a bit sometimes and I need extra review steps. I like to architect / plan with opus and code with grok… like the price per performance.”
r/cursor · hybrid-stack pattern
“Grok 4.5 is fast, cheap and super effective at what I need it to do.”
u/welsh_cthulhu · ~109 upvotes (corpus top comment)
Read the room carefully.
Pre–Opus 5, “Grok vs Opus” meant Grok 4.5 vs Opus 4.7/4.8. Launch-day Opus 5 discourse is still mostly “vs Fable / vs 4.8,” not a settled Grok 4.5 bake-off. Treat hybrid-stack advice as durable; treat “Grok beats Opus on quality” as pre-5 anecdotal.
5. Head-to-head
Dimension
Grok 4.5
Claude Opus 5
What it is
xAI flagship for code + agents; thrift-first
Anthropic Opus tier; near Fable at half Fable cost
List price (in/out)
$2 / $6 per 1M (<200k)
$5 / $25 per 1M
Context
500k (long-context surcharge ≥200k)
1M at standard Opus rates
AA cost / task (Intel Index)
~$0.31
~$2.03 (max)
Intelligence ceiling
Near-frontier (~54 AA)
Frontier-tied (~61 AA max)
Agent coding
Strong thrift; TB ~83%
Higher ceiling; TB ~89% max
Knowledge / judgment work
Solid, not the headline
Launch SOTA on several agentic KW benches
Effort controls
Low / medium / high
Low → max + Fast mode
Best for
High-volume agent loops, Cursor thrift
Hard tickets, planning, review, KW agents
Install / access
Grok Build, Cursor, xAI API
Claude API, Claude Code, Max default
6. Choose if / emerging stack
Choose Grok 4.5 if
You measure success in $ / merged PR or $ / agent session.
Workloads are high-volume coding agents (Cursor, Grok Build, OpenCode-style loops).
You’re fine with slightly more human review for a large cost cut.
You already run a stronger planner/reviewer model above it.
Choose Claude Opus 5 if
You need the highest available intelligence without Fable’s full bill.
Tasks are hard debugging, ambiguous specs, finance/legal/knowledge work.
A failed agent run costs more than the token delta vs Grok.
The emerging stack
Community practice (especially r/cursor) is not “one model forever.” It’s a pipeline:
Plan / architect on Opus 5 (or Fable 5 when the problem is truly frontier).
Execute long coding loops on Grok 4.5 for token thrift.
Review / gate with Opus 5 (or a human) before merge.
That pattern showed up repeatedly before Opus 5 shipped (plan on Opus 4.8, code on Grok).
Opus 5 upgrades the planner/reviewer slot without changing the economic logic of the executor slot.
Rule of thumb.
If an agent will burn millions of tokens overnight, start on Grok and promote failures to Opus 5.
If a single session can lose a day of eng time when wrong, start on Opus 5 and only demote to Grok after the path is clear.
7. Caveats
Opus 5 is day-zero. Independent third-party cost-per-task numbers will move as AA and harnesses re-run.
Harnesses dominate scores. Terminal-Bench / SWE numbers shift with agent scaffolding; compare same harness.
Long-context surcharge on Grok. At ≥200k prompt tokens, Grok’s rate doubles — still usually under Opus output rates, but model the break-even.
EU / access. Techmeme and launch notes flagged Grok 4.5 availability limits in the EU; check your console.
Fast mode / effort. Opus 5 Fast is ~2× price; max effort can spend more tokens than Grok even when quality is worth it. Log $ / task in your own product.
This is not a latency post. Token rates matter; tok/s and queueing matter too — measure where you deploy.