UPDATE: I added a short statement from stylus-maker Adonit below.

SAN FRANCISCO — Tim Ritchey is an expert in iPad styluses — the pressure-sensitive digital pens that draw with pinpoint accuracy on an iPad.

Ritchey works for Adonit, a company that makes a line of Bluetooth styli for the iPad. His job title is “OS architect.” He knows his stuff.

In the middle of a session at this week’s Worldwide Developers Conference, he heard something that prompted him to send a panicky note to his colleagues in Slack, the popular messaging system.

“Oh shit!” he said.

Steve Jobs famously pledged that Apple would never ship an iOS device with a stylus, but there’s mounting evidence that the company is working on a new and bigger work-oriented iPad that will come with a stylus.

A couple of big clues dropped this week at WWDC.

As the explosive growth of the iPad slows, Apple seems keen to expand the market into the professional space. On the software side, Apple is teaming up with IBM to develop apps for enterprise. In hardware, there are clear signs of a bigger iPad with a 12.9-inch screen, including hardware leaks out of China. A bigger iPad with a stylus would be well suited for precision work in a range of creative professions, from graphics to 3-D.

Earlier this week, Ritchey was watching the “What’s new in Cocoa Touch” WWDC session, which details some of the new technologies added to iOS 9. Cocoa Touch is the underlying UI framework used by software programs that run on iOS.

Presented by Jason Beaver, a senior engineering manager in Apple’s iOS group, a video of the talk is available online.

In the middle of the talk, Beaver describes a couple of major changes to the way touch-sensitive screens handle finger touches (scrub to the 13:54 mark in the video). Beaver said iOS 9 “dramatically reduces” what’s known as the touch-to-display latency, a millisecond lag between when you touch the screen and the screen reacts to your touch.

Under most circumstances, the touch-to-display latency is imperceptible, but it’s there, and it can sometimes be seen if you move your finger fast enough.

In addition, Beaver said iOS 9 now includes “touch prediction,” which he described as “a very sophisticated algorithm that looks at a touch’s velocity, acceleration and curvature to see where the touch is headed.”

This is what caused Ritchey to send his “oh shit” message on Slack.

Predictive touch technology is the key technology behind all styluses — both computer and iPad. Touchscreens and drawing tablets generally aren’t accurate enough for precision work unless they have predictive touch technology. Predictive touch dramatically improves the speed and accuracy of a pen.

“A lot of the software that drives styluses is predicting where the touch point is based on the movement of the stylus, its angle and other factors,” Ritchey said.

Another big clue was revealed earlier this week. During Monday’s WWDC keynote, Apple showed off new drawing capabilities in iOS 9’s Notes app. The Notes app, which is currently used to make, well, notes, has gained support for drawings and doodles. Users can make drawings and squiggles with their fingers. A selection of tools allows different brush styles and colors, and there’s a ruler to keep sketches straight.

It’s unlikely the Notes app will be used for the kind of serious work Apple is prepping the iPad Pro for, but it shows iOS 9 includes a drawing engine.

Taken together, these are strong indications that Apple is looking at styluses, Ritchey said.

“These are the kinds of things you want in place if you were going to come out with a stylus,” he said.

Developer Giovanni Donelli agreed with Ritchey’s assessment. Adding drawings and predictive touch to iOS are clear signs that Apple is preparing for a precision stylus.

Donelli is the co-creator of Astropad, an app that turns an iPad into a graphics tablet for the Mac.

But where Adonit, Wacom and other stylus makers should be nervous, an Apple stylus is great for Astropad. It will make their app even better.

“It will really help with creative tools,” Donelli said. “An Apple stylus will really help us compete with Wacom.”

Update: A spokeswoman for Adonit said the company “actually welcomes an Apple stylus,” and forwarded the following from Ian Shirey, Adonit’s Chief Strategy Officer:

At Adonit, our products turn the iPad from a consumption device into a productivity device. Based on current rumors, it appears Apple shares our thinking and is staging a major shift in how we use tablets in the workplace. We welcome the possibility of an Apple stylus entering our market, it would only reaffirm our belief of the need for such tools exists among consumers and the workplace.

I don’t want to be cynical, but this is what incumbents always say. Nonetheless, they are right. It does validate the market and if Adonit and others differentiate their products from Apple’s, or innovate faster, they might do better than ever. I sincerely wish them the best of luck.