Docs updates September (#38796)

Closes #ISSUE

Release Notes:

- N/A

---------

Co-authored-by: Katie Geer <katie@zed.dev>
Co-authored-by: Marshall Bowers <git@maxdeviant.com>
Co-authored-by: David Kleingeld <davidsk@zed.dev>

docs/src/ai/plans-and-usage.md

@@ -1,8 +1,5 @@
 # Plans and Usage
 
-To view your current usage, you can visit your account at [zed.dev/account](https://zed.dev/account).
-You’ll also find usage meters in-product when you’re nearing the limit for your plan or trial.
-
 ## Available Plans {#plans}
 
 For costs and more information on pricing, visit [Zed’s pricing page](https://zed.dev/pricing).
@@ -11,29 +8,20 @@ Please note that if you’re interested in just using Zed as the world’s faste
 
 ## Usage {#usage}
 
-- A `prompt` in Zed is an input from the user, initiated by pressing enter, composed of one or many `requests`. A `prompt` can be initiated from the Agent Panel, or via Inline Assist.
-- A `request` in Zed is a response to a `prompt`, plus any tool calls that are initiated as part of that response. There may be one `request` per `prompt`, or many.
+Usage of Zed's hosted models is measured on a token basis, converted to dollars at the rates lists on [the Models page](./models.md) (list price from the provider, +10%).
 
-Most models offered by Zed are metered per-prompt.
-Some models that use large context windows and unlimited tool calls ([“Burn Mode”](./models.md#burn-mode)) count each individual request within a prompt against your prompt limit, since the agentic work spawned by the prompt is expensive to support.
+Zed Pro comes with $5 of monthly dollar credit. A trial of Zed Pro includes $20 of credit, usable for 14 days. Monthly included credit resets on your monthly billing date.
 
-See [the Models page](./models.md) for a list of which subset of models are metered by request.
+To view your current usage, you can visit your account at [zed.dev/account](https://zed.dev/account). Information from our metering and billing provider, Orb, is embedded on that page.
 
-Plans come with a set amount of prompts included, with the number varying depending on the plan you’ve selected.
+## Spend Limits {#usage-spend-limits}
 
-## Usage-Based Pricing {#ubp}
+At the top of [the Account page](https://zed.dev/account), you'll find an input for `Maximum Token Spend`. The dollar amount here specifies your _monthly_ limit for spend on tokens, _not counting_ the $5/month included with your Pro subscription.
 
-You may opt in to usage-based pricing for prompts that exceed what is included in your paid plan from [your account page](https://zed.dev/account).
+The default value for all Pro users is $10, for a total monthly spend with Zed of $20 ($10 for your Pro subscription, $10 in incremental token spend). This can be set to $0 to limit your spend with Zed to exactly $10/month. If you adjust this limit _higher_ than $10 and consume more than $10 of incremental token spend, you'll be billed via [threshold billing](./billing.md#threshold-billing).
 
-Usage-based pricing is only available with a paid plan, and is exclusively opt-in.
-From the dashboard, you can toggle usage-based pricing for usage exceeding your paid plan.
-You can also configure a spend limit in USD.
-Once the spend limit is hit, we’ll stop any further usage until your prompt limit resets.
-
-We will bill for additional prompts when you’ve made prompts totaling $20, or when your billing date occurs, whichever comes first.
-
-Cost per request for each model can be found on [the models page](./models.md).
+Once the spend limit is hit, we’ll stop any further usage until your token spend limit resets.
 
 ## Business Usage {#business-usage}
 
-Email [sales@zed.dev](mailto:sales@zed.dev) with any questions on business plans, metering, and usage-based pricing.
+Email [sales@zed.dev](mailto:sales@zed.dev) with any questions on business plans.