How to keep career momentum when switching jobs?

Since you're joining at mid level, the good news is that a lot of the momentum is coming from individual skill.

The main behavior I'd demonstrate to show that you're serious is being proactive.

• Don't wait to take up more tasks for your project(s): just take them.
• Someone has a question around your domain? Give them an answer and potentially some references.
• Code isn't as clean as you could be? Fix it along the way of your current task.
• Are there tasks on someone's else project that could be parallelized with an extra set of hands? Jump in.

Being close to E5 at Meta means nothing to your Anthropic manager: so you need to set the baseline that you're doing more than what's needed beyond E4/mid-level and that impression can be seen. If your manager views your baseline as an average mid-level engineer, they likely won't take you as seriously. Once that baseline is set, I'd look to the following two:

• Ask your manager for opportunities to lead projects to show senior-level compotency. If you really want the senior-level promo, bring this up every 1:1 or every other 1:1.
• While you're proactively poking around the broader scope of the company/team, see if there's any gaps you can help fill around existing projects when it comes to project leadership. Why wait for your manager to give you opportunities when it could be faster finding them yourself?

A lot of the onboarding course is about this! I like the framing of having a "trust score" when you start at a company, and you want to quickly move that score up: Why Onboarding Matters.

Two things I'd add to Jonathan:

• Explicitly state that you want to move quickly (and therefore are eager for feedback) in your first few meetings, and talk about how this will manifest in your onboarding doc.
• Land code quickly in the Anthropic job: Rack Up Small Wins. Do this while also building up context to owning a significant project.