This article was more true than not a year ago but now the harnesses are so far past the simple agent loop that I'd argue that this is not even close to an accurate mental model of what claude code is doing.
I'd say it's similar to how a "make your own relational DB" article might feature a basic B-tree with merge-joins. Yeah, obviously real engines have sophisticated planners, multiple join methods, bloom filters, etc., but the underlying mental model is still accurate.
Here’s a reframing:
If you asked people “what would you rather work with, today’s Claude Code harness with sonnet 3.7, or the 200 line agentic loop in the article with Opus 4.5, which would you choose?”
I suspect many people would choose 3.7 with the harness. Moreover, that is true, then I’d say the article is no longer useful for a modern understanding of Claude Code.
3.7 was kinda dumb, it was good at vibe UIs but really bad at a lot of things and it would lie and hack rewards a LOT. The difference with Opus 4.5 is that when you go off the Claude happy path, it holds together pretty well. With Sonnet (particularly <=4) if you went off the happy path things got bad in a hurry.
But skills do improve model performance, OpenAI posted some examples of how it massively juiced up their results on some benchmarks.
It's not.
I've done this (although not with all these tools).
For a reasonable sized project it's easy to tell the difference in quality between say Grok-4.1-Fast (30 on AA Coding Index) and Sonnet 4.5 (37 on AA).
Sonnet 3.7 scores 27. No way I'm touching that.
Opus 4.5 scores 46 and it's easy to see that difference. Give the models something with high cyclomtric complexity or complex dependency chains and Grok-4.1-Fast falls to bits, Opus 4.5 solves things.
Look at https://github.com/SWE-agent/mini-swe-agent for proof
There’s a reason Cursor poached Boris Cherney and Cat Wu and Anthropic hired them back!
I actually wrote my own simple agent (with some twists) in part so I could compare models.
Opus 4.5 is in a completely different league to Sonnet 4.5, and 3.7 isn't even on the same planet.
I happily use my agent with Opus but there is no world in which I'd use a Sonnet 3.7 level model for anything beyond simple code completion.
https://www.tbench.ai/leaderboard/terminal-bench/2.0 says yes, but not as much as you'd think. "Terminus" is basically just a tmux session and LLM in a loop.
For the longest time, Claude Code itself didnt really use subagents much by default, other than supporting them as a feature eager users could configure. (Source is reverse engineering we did on Claude code using the fantastic CC tracing tool Simon Willison wrote about once. This is also no longer true on latest versions that have e.g. an Explore subagent that is actively used.)
I was having codex organize my tv/movie library the other day by having it generate. most of the files were not properly labeled. I had codex generate transcripts, manually search the movie db to find descriptions of show episodes, and match the show descriptions against the transcripts to figure out which episode/season the show belonged to.
Claude Code could have parallelized those manual checks and finished that task at 8x the speed.
(Should have 2025 in the title? Time flies)
I find it doing what I in the past had to interrupt and tell it to do fairly frequently now
CC has built in subagents (including at least one not listed) that work very well: https://code.claude.com/docs/en/sub-agents#built-in-subagent...
this was not the case in the past, I swore off subagents, but they got good at some point