I Made Grok 4.5 My Default Coding Model for One Client Week

On July 8, Cursor and SpaceXAI put Grok 4.5 in front of every Cursor subscriber who would click the model picker. The pitch was simple: frontier-ish coding and agent work, trained with real Cursor interaction data, cheap enough that token anxiety stops being the main character.

I did what I always do when a tool claims it belongs in the daily path. I made it the default for one week on a real client repo and wrote down what broke.

This is not a benchmark re-score. It is a work log.

The task I actually ran

Client context, sanitized: a Next.js App Router publication with content validation, MCP servers for ads and analytics reads, and a pre-commit asset pipeline. The week had three jobs that match how I actually bill time.

1. Ship a feature branch with two new MDX routes, shared components, and schema fields that had to pass bun run validate.
2. Debug a flaky integration where an MCP tool returned partial JSON and the agent kept "fixing" it by inventing keys.
3. Drive a multi-file refactor that touched route handlers, a Zod schema, and a small TypeScript helper without breaking static generation.

I used Cursor as the shell the whole week. Grok 4.5 as the default model. Same MCP config I already trust. No special harness beyond what a mid-size agency repo already has.

What worked, with receipts

Speed on the boring middle. Autocomplete-plus-edit on component props, frontmatter keys, and test stubs felt fast. Not magically smarter than Opus-class on hard architecture. Noticeably cheaper per loop when I was iterating ten times on the same file. For the kind of work that is 70% of a billable day, that matters more than a one-point leaderboard bump.

Cursor-native habits. This is the underrated part of "trained with Cursor data." The model was less confused by multi-cursor edits, partial selections, and "apply this diff but keep my comment." That is not a general intelligence claim. It is a product claim, and on this repo it held.

Price as a product feature. At roughly $2 input / $6 output per million tokens (and lower on cached), I stopped doing the mental math that makes people under-prompt. I asked for the second rewrite. I asked for the third. The quality of the session went up because I stopped rationing turns. That is a real effect, even when single-shot quality is a wash.

Rough week spend on the client branch, all-in model cost through Cursor: under what a single heavy Claude Max-style day used to burn on comparable volume. Your numbers will differ. The direction did not.

What broke first

Unsupervised multi-file refactors. When I pointed it at "migrate these three modules and keep generateStaticParams honest," it produced a plausible plan and then a half-applied migration. Two files updated. One left mid-state. Tests red. Claude Code on the same prompt the next morning finished the graph more cleanly, with fewer "I will fix the types in a follow-up" lies.

Confident wrong tools. On the MCP JSON bug, Grok 4.5 was eager. It rewrote the client twice before it agreed to log the raw payload. Claude's slower, slightly pedantic loop would have asked for the log earlier. Eager is not free. Eager costs review time.

Long context discipline. On a chat that had already eaten a big schema dump, it started compressing my constraints into vibes. I had to re-paste the Zod refine rules mid-thread. Not unique to Grok. Worse here than my Sonnet baseline on the same thread length.

How it compares on the jobs that matter

The posture split from the public discourse is real. Cursor assumes you are editing. Claude Code assumes you are delegating. Grok 4.5 inherits the Cursor posture even when you ask it to act like an agent. That is not a bug if you wanted a co-pilot. It is a bug if you wanted a night-shift senior.

Verdict

Buy Grok 4.5 as a default inside Cursor for iterative product work if you already live in that editor and your pain is token cost plus turn latency.

Wait before making it the only model for unattended multi-file agents or production refactors that touch codegen boundaries. Keep a heavier model one hotkey away.

Skip if your whole workflow is terminal-agent and you already have Claude Code tuned. Switching shells just to chase a model is a tax.

I am not deleting Claude from the stack. I am not writing a "Grok won coding forever" post. I am changing my default for the 70% path and keeping the expensive brain for the 30% path that ships the scary PR.

Six months ago I would have told you to pick one model and learn it deeply. I no longer believe that is the right advice for coding agents. The July wave made routing the skill. Grok 4.5 is a strong cheap route, not a religion.

What I will re-test in 30 days

1. Same multi-file refactor with whatever patch they ship after the first wave of forum complaints.
2. Token spend on a pure greenfield app versus this brownfield content site.
3. Whether "double usage first week" promo pricing was hiding a bill shock at steady state.

If any of those flip the verdict, I will update this page in public. That is the deal on The Stack.

Sources

• Cursor, Introducing Grok 4.5
• DevOps.com on Grok 4.5 pricing and Cursor collab
• Nimbalyst, Claude Code vs Cursor posture
• Prior Promptway stack note: Connecting Claude to Google Ads and GA4 via MCP